Earth's “Bigger Cousin” Detected

Artist's conception of the newly discovered planet around Gliese 876 -- it is shown as a hot, rocky, geologically active world glowing in the deep red light of its nearby parent star.Credit: Trent Schindler, National Science Foundation.

Astronomers
announced today the discovery of the smallest planet so far found outside of
our solar system. About
seven-and-a-half times as massive as Earth, and about twice as wide, this new
extrasolar planet may be the first rocky world ever found orbiting a star
similar to our own.

"This
is the smallest extrasolar planet yet detected and the first of a new class of
rocky terrestrial planets," said team member Paul Butler of the Carnegie
Institution of Washington. "It's like Earth's bigger cousin."

Currently
around 150 extrasolar planets are known, and the number continues to grow. But
most of these far-off worlds are large
gas giants like Jupiter. Only
recently have astronomers started detecting smaller massed objects

"We
keep pushing the limits of what we can detect, and we're getting closer and
closer to finding Earths," said team member Steven Vogt from the
University of California, Santa Cruz.

The
discovery of Earth's distant cousin was announced today at a press conference
at the National Science Foundation in Arlington, Va.

The
new planet orbits Gliese 876,
an M dwarf star 15 light years away in the constellation Aquarius. The "super-Earth" is not alone: there are two other planets - both
Jupiter-sized - in the same system.
This third world was detected by a tiny extra
wobble that it caused in the central star.

From
this wobble, the researchers measured a minimum mass for the new planet of 5.9
Earth masses. The planet orbits makes a
full orbit in a speedy 1.94 days, implying a distance to the central star of 2
million miles - or about 2 percent of the distance between the Earth and the
Sun.

Orbiting
so close to its star, scientists speculate that the planet's temperature is a
toasty 400 to 750 degrees Fahrenheit (200 to 400 degrees Celsius). This is likely too hot for the planet to
retain much gas, like Jupiter does.
Therefore, the planet must be mostly solid.

"The
planet's mass could easily hold onto an atmosphere," said Gregory Laughlin
from UC Santa Cruz. "It would still be considered a rocky planet, probably
with an iron core and a silicon mantle. It could even have a dense steamy water
layer."

A paper detailing these results has been submitted to The Astrophysical
Journal.